Protein arginine methylation, which is specifically mediated by protein arginine methyltransferases (PRMTs), represents one of the most important and ubiquitous posttranslational modifications in biological regulation. PRMTs are involved in a variety of cellular processes including epigenetic reprograming, RNA splicing, signal transduction, and DNA repair. Significant amounts of evidence have shown that altered PRMT expression and activity are associated with tumorigenesis, inflammation, diabetes, neurological disorders, and many other recalcitrant disease conditions. PRMTs are highly promising molecular targets in the search for new chemotherapies. However, functions of PRMT enzymes in regulating signaling cascades and disease pathways are poorly understood. Molecular mechanisms of PRMTs in major oncology processes are not yet defined. Importantly, quality chemical leads are scarce for effective targeting of arginine methylation, which significantly hampers current pharmaceutical advance. This research project is aimed at developing novel chemical biology strategies and organic probes as powerful mechanistic means to interrogate PRMT function in key biological pathways and disease processes. We will innovate multiple lines of strategic designs to determine substrate recognition mechanisms of PRMTs and illuminate functional interplays among key histone modifications in epigenetic fate regulation. Great efforts will be engaged in developing potent and subtype-selective small molecule inhibitors with privileged structural scaffolds that can be used to selectively block the enzymatic activity of the major PRMT subtypes. A diversity of library compounds will be screened; chemical analogs will be synthesized; and best leads will be characterized for their pharmacokinetics and pharmacodynamics properties. Detailed biochemical, cellular, and in vivo studies will be conducted in a systematic way to define structure-activity relationship and mechanism of action with the goal of generating a new generation of potent, subtype-selective PRMT inhibitors. Altogether, the projected research will yield in-depth understanding of PRMT-regulated disease mechanisms and translate laboratory leads into clinical candidates for the treatment of PRMT-related ailments.